1. Field of the Invention
The present invention relates to a heat treatment jig to be used for carrying out a heat treatment in a vertical heat treatment apparatus to be used in a semiconductor manufacturing process, and to a method and an apparatus for measuring the shape of such a heat treatment jig, to confirm that the jig has a shape reducing crystal defect or damage of a semiconductor wafer.
2. Discussion of Background
A process for treating a semiconductor wafer (hereinafter referred to as a “wafer”) in a semiconductor manufacturing process, includes a heat treatment process using high temperature such as an annealing treatment, an oxidation treatment or a diffusion treatment, and in such a heat treatment process, a vertical heat treatment apparatus is used according to upsizing of a wafer.
In this type of vertical heat treatment apparatus, a holding jig named “boat” is used, which is constituted by a pair of end plates 1, 1 positioned at the top and the bottom as shown in FIG. 1, and three or four supporting rods 2, 2 . . . provided between the pair of end plates 1, 1, on which a plurality of grooves 4 is formed as shown in FIG. 2 for positioning a wafer 3. There has been a problem that in a case where a wafer 3 is held by such a boat and subjected to a heat treatment, since the weight of the wafer 3 is supported at contact portions with the grooves 4 of the boat, when a heat is applied to the wafer 3, there occurs a positioning shift due to a thermal expansion difference between the materials of the wafer 3 and the boat or due to deflection of the wafer 3 by its own weight, or there forms a shearing stress of the wafer 3 by its own weight, and they cause damages or crystal defects (slip) in the wafer 3.
In order to solve such problems, a method is proposed, in which instead of using grooves 4 for holding a wafer 3, a circular doughnut-shaped heat treatment jig 5 shown in Patent Document 1 and in FIG. 3 of this application, is used for holding the periphery of the wafer 3 as shown in FIG. 4, and the grooves 4 of the boat are used for supporting the periphery of the heat treatment jig 5 as shown in FIG. 5.
Further, as shown in Patent Document 2, when a wafer is placed on a heat treatment jig, the wafer is deflected by its own weight and a shearing stress is applied to a portion of the wafer in contact with the inner periphery of the jig, which causes crystal defects of the wafer, and the document proposes means for preventing such crystal defects.
Further, as means for more efficiently holding the periphery of a wafer, Patent Document 3 proposes a method of arranging contact portions of the outer periphery of the wafer so that they are outside a region for producing semiconductor devices, and a method of forming each wafer-holding surface into a tapered shape toward the center so as to have a line contact with the wafer instead of a face contact, to reduce occurrence of damages or crystal defects.
These heat treatment jigs are made of a material such as a fused quartz, a synthetic quartz, a sintered silicon carbide coated with the same material by CVD, a silicon carbide that is so-called solid product produced by a CVD method, silicon or carbon.
Patent Document 1: JP-A-7-45691
Patent Document 2: JP-A-9-199438
Patent Document 3: JP-A-2005-101161
However, in a semiconductor manufacturing process, a treatment such as an anneal treatment in which the heat treatment temperature is at least 1,200° C., becomes widely used and defect-free requirement for wafers becomes more strict, and consequently, more damages or crystal defects are detected even with a heat treatment jig having a conventionally proposed shape.
This is because such conventionally proposed shapes of heat treatment jigs are ones considering only deformation of a wafer but not considering deformation of the heat treatment jig itself by its own weight, or deformation of the heat treatment jig in a higher temperature region. Further, this is also because such shapes are ones only considering deformations in a radial direction but not considering deformation in a circumferential direction that is determined by the number, positions and the shape of grooves of a boat for holding the heat treatment jig itself.
Proposal of an optimum shape of heat treatment jig considering a deformation due to the heat treatment jig by its own weight or due to heat, can be determined by a simulation using e.g. a finite element method.
When a heat treatment jig having a shape also considering such a deformation by a simulation is produced, it is necessary to confirm whether the finished shape has a predetermined accuracy. In this step, a conventionally used three-dimensional measurement tool has a flat stage to be used for placing a heat treatment jig being an object to be measured, and accordingly, the heat treatment jig is deflected by its own weight to prevent accurate measurement. Further, in a case of point-contact type profiler, the heat treatment jig is deformed by a contact pressure to prevent accurate measurement. Further, in order to prevent the above-mentioned damages or crystal defects, it is essential to determine a three-dimensional shape of a surface of the heat treatment jig to be used for placing a wafer. However, on a flat stage, manufacturing accuracy of the opposite surface of the jig, more specifically, parallelism, may affect the measurement, and accurate measurement becomes difficult.
It is possible to adjust a measured shape considering these deformation or parallelism. However, such a adjustment requires excessive steps and significantly deteriorates productivity.